At present, methods for identifying a living body include: fingerprint identification, iris identification, face identification, vein recognition, heart rate identification and the like.
Most of the fingerprint identification methods are based on the following principle: a fingerprint is acquired by a fingerprint acquisition unit, a fingerprint image is generated from the acquired fingerprint, then the fingerprint image is processed to extract fingerprint characteristic points, and finally the fingerprint characteristic points are stored for specific application of the fingerprint (for example, for use in fingerprint authentication).
Traditional fingerprint acquisition methods include: optical fingerprint acquisition, capacitive fingerprint acquisition and ultrasonic fingerprint acquisition. FIG. 1 is a schematic structure diagram of a traditional optical fingerprint acquisition device, which mainly uses the refraction principle and the reflection principle of light. Specifically, a finger 4 is put on an optical lens 5 (for example, a triangular prism); when the finger 4 is exposed to light from a built-in light source 6, the light is incident into the optical lens from the bottom thereof and emergent from the optical lens; and the emergent light will have different refractive angle and brightness of reflected light on rugged lines of the fingerprint on the surface of the finger 4. The light is projected, by the optical lens, onto a sensor 7 (for example, a charge-coupled device) to form a digital multi-gray fingerprint image which can be processed by an algorithm of a fingerprint device and in which ridge lines (lines with certain width and trend in the fingerprint image) are presented as black and valley lines (recesses between ridges) are presented as white.
The light source 6 and the sensor 7 of this optical fingerprint acquisition device must be arranged at specific positions, and it is necessary to use the optical lens 5 so that light emitted from the light source 6 to the finger 4 can reach the sensor 7 after being reflected. Furthermore, only the light emitted in a specific angle from the light source 6 can be received by the sensor 7 after being reflected. That is, if light reflected from the optical lens deviates from the reception range of the sensor 7, fingerprint information cannot be acquired.
The aforementioned optical acquisition device requires direct contact between a part, which is to be identified, of a living body and the acquisition device, making the detection very inconvenient. In addition, usually, identification of an iris or a face cannot be achieved by this device, greatly limiting the application of such an optical acquisition device.